The ERT2 chain is good, that is what I use and has lasted 2 seasons, yes it is recommended that you replace sprokets with chain, but I have just replaced the chain before if the sprokets look good. If I was running a 13 and had the possibility of one day going to a 15, I would cut the chain if needed, but I would do it near the end of adjustment on the tight side so you have ample room to loosen to go back to a 15. the only problem you may run into is when the chain streches, as it will the first couple rides, if you reach the end of adjustment and the chain is still too loose, you may need to take another link off.
Another thought, if you still have the 14T, put the 14 on and cut the chain so you are at middle travel in adjustment, you should have enough adjustment to go up or down one tooth.
734 09 Raptor
Meglodon by Bo,KW springs, Web 4 Cam, 54mm TB, 105.5mm CP cylinder, 14:1 CP,Barkers Inframe,Dynatek Coil,PC V,Dynatek Programable ignition,CCP stabilizer,+5 swinger,Boss Noss Sys, Direct Drive Lock-up, KDS Evac valve,HID Light conversion,SPAL fan
Tuned by EHS Racing 78hp 55Tq