How did you feel upon completion of that effort and workout?
Are you consistent in your nutrition, recovery, training setup and such?
I felt normal after workout, no struggling, a little soreness in legs for 1-2 hours
OK, that’s interesting.
How about my second question?
second part is ok too, but sometimes my kickr goes power up like for 160-170 for no reason or while my cadence dropped to 85 because I try to sustain 90 or more
Depending on the specific Kickr model (anything other than the current 2020 V5), are you calibrating it? If so, how often?
Calibrated once last week ago, yeah, kickr 2020 v5
Which basic plan? Did you use the plan builder?
They vary - Low, Medium and High volume.
They can also be focused on certain events - Gran Fondo, Rolling Road Race, off-road, etc?
yes I did, I had selected triathlon sprint if Im not mistaken for low volume 2-3 workouts per week
The problem is that with properly set FTP, even if you are completely new to riding a bike (not even training) doing something like a couple of 15min@90% should be doable without any problem. I would think that your ramp test is way off due to the huge anaerobic contribution to your result, hence overinflated FTP. People have a natural predisposition to be fast-twitchers, as slow-twich muscles require some training.
But 1.5 year of riding a bike should be more than enough. I remember a track rider who has 2000W sprint has FTP of 240W so the proportion is quite similar. But not being able with ease 15 min sst intervals has probably bo relation to phenotype but the issue is somewhere else.
Yeah if you can’t do SST it’s because your estimated ftp is way off. It has nothing to do w being inclined to sprint or be a climber, etc.
@hdas ‘s point is that if you’re a great sprinter, focus on being a great sprinter. Not much point in trying to be a climber (or whatever)
The OP seems pointed at Tri with a mention of a shorter TT (see quote below).
In either of those cases, sprinting seems all but useless to me. Despite the classification the OP has selected, sprinting seems like a misplaced focus with those events in mind.
I would generally agree if you can’t do SS your FTP is probably too high. However, given you are new to training and your FTP isn’t unrealistically high; perhaps the FTP is correct and your just mentally giving up on sweetspot too early and you can actually physically do it, you just have to put your mind to it 
Sprint means triathlon sprint distance. 750 swim 5k run 20k bike
Yes, I know that well… and it has nothing to do with my point above.
(Notice the specific elements I quoted above.)
Just because “sprint” is in that event name, doesn’t mean that something like your 15-30 second power data (often related to “sprinting” in general discussion) is at all relevant for the training discussed here. That aspect is the point seemingly recommended in this comment:
I am trying to get to the point that your 15-30 second power, and your mention “I’m naturally a sprinter” is sidetracking some suggestions above to push for more “sprint” power focus (not your event name/type) as opposed to the Sweet Spot or other training emphasis.
No matter the name of your event, your performance (good or bad) at the 15-30 second power range is not relevant to even the shorter 20k bike leg. It will more likely be a high Threshold effort, well short of “sprinting” referenced from you and the others apparently advocating a focus on your “sprint” training.
Clear as mud? 
I get that to some extent, but I think there’s a big leap between knowing your strengths and never trying to improve upon anything else. Not to mention being a “natural anything” is sort of a moot point for amateurs- most of us have a lot of room to improve on all aspects of our fitness, and the value of each of those is largely subjective to our goals.
I haven’t done a TR tri plan in a while, but from memory they start off with longer durations than the regular SSB plans (perhaps assuming those riders would be more naturally inclined towards those sorts of efforts?) I wouldn’t be shy about knocking them down a few %, adjusting your FTP if you feel it’s appropriate, or working your way up from shorter intervals especially if you’re newer to indoor training- I’d rather start more conservatively than beat myself up about failing workouts all the time.
With that said, the screenshot the OP posted doesn’t look terrible to me- getting through it with a few backpedals/drops is far from a complete failure, and while it’s a bit rough and might give you some ideas of what to work on, not every workout is going to look perfect. 
H said that before OP said they want to train for a 20km Leg for a sprint triathlon.
I agree with H’s point, that if you have a disposition to be a good sprinter, focusing on developing low end power probably will be more profitable for bicycle racing than trying to build your aerobic engine (essentially you just need to not get dropped). This doesn’t mean neglect it, but don’t allocate the majority of your training time to developing it relative to focusing on your strength.
The 60min ftp obsession is fun for training and data lovers, but it’s not essential for winning lower category bike races (mostly all races outside of domestic elite, when teams matter, are just won in sprints). Sprint through 1-5min power is most important.
Obv OP must focus on boosting ftp if they want to be competitive in triathlon.
I just want to get as much fit as possible and sprint triathlon event just part of it. Without any events a little bit hard to get along with workouts and sticking to the plan. I wanna do gran fondo, crits, or just endurance long rides. So I think its important to build aerobic base
hey Hardcore! I may have missed this, but the argument seems to be whether you need sweet spot or not. If you are struggling, can you find some tempo workouts first? like:
3 x 10m @ 85-90%, with 5m rest between…
If that is too easy, extend them out, towards 3 x 20m or 2 x 30m and really focus on 90%
Then go back to the shortest SS that you can find, and start Small! 4 x 8m @ 93-95% with 4m.
Eventually you will build up towards the workouts you’re aiming at.
Just sounds like the workout is a bit too hard right now. DOnt give up tho, you’ll get there!
Good luck!
Brendan
So you perform a ramp test and get an FTP that you can’t hold 95% of for more than 13 to 15 minutes? Your FTP is probably about 95% of the target power of that workout.