line length is a very personal / style / conditions question. 2 Years ago I was very big friend to go with very small race kites in no wind, but on up to 27 m lines. All on Foil-Raceboards. Last year I tried my 15 m² Chrono down to 12 m lines by 1 m steps. Actually I landed inbetween 15-16 m for me and this kite. But as I said this is very personal compromise to find. Around 15 m line every single meter changes behavior noticeable.
If you feel your kite could change wind window faster, I think it is worth to try first 18 m and if it is still to slow than 16 m or directly to 16 m, but be aware this is a very big step. 15 m and beneath work, but will be very radical and you will get problems in the very lowend winds as the loops for the start you will have to partially stall the kite to be able to turn the kite. And around this you also start to change trimm of the kite noticeable as line V is smaller and the kite may tend to more tip collapse if not corrected. On the other hand it is awesome when a 15 m² kite in 6 knts can feel like a 10 m² kite in 20 knts if lines are just short enough.
Good luck, testing and best learn splicing yourself if you want to try and change a lot.
and sorry don't know the R1v1 but would expect it is better to not go to short with this one, Chrono v1 is for sure easier here. Tried also I think 13 m² and 15 m² Sonic Race on about 15 m but for me partially good partially also to short.