It is true that the higher the temp the quicker the shrimp will grow and reproduce, the trade off is that with the quicker growth and breeding comes earlier death. Dwarf shrimp don't have long lives any way so speeding up their life cycle is not always a good thing. Keep in mind too that too high a temp will also stress the shrimp, which can pave the way for secondary infections and diseases to take hold.
My tanks which house fish and shrimp (cherry shrimp and quite a few Australian native species of shrimp) have the tank temp set at 22 degrees cel, which in winter the water may get down to 18 or even 16 degrees cel (especially further way from the heater) and in summer these same tanks with the heater turned off can soar to 30+ degrees. The 30+ is not ideal but the shrimp and fish take it all in their stride, I also run extra air in my tanks, have heavy surface agitation from the filter return and open topped tanks to allow better temp transfer.
As already stated there will be a bit of trial and error to find exactly works for you and your setup with the shrimp.