How long will the climb in the race take you (in minutes)?

It's a bit late for this, but try doing some efforts to boost your FTP (functional threshold power). You've already done some longer intervals (3x15'). Try 5x5' at 105-108% over FTP. (Your FTP is your hour power, so maybe hit an effort that you could sustain for a 20-30min TT if you're going by RPE or HR). 1' rest. This is key (the 1'). You can also do 4x8' with 2 min rest, but these are done around FTP or a little below, but not above. You obviously have a great endurance base and can handle the mileage. Now it's time to teach yourself how to quickly recover after hard efforts that come from accelerations during a race.

On another day, do hill repeats on that climb you have that's close to the one you'll see at the race.