'and' or 'to' to specify a range

I have the following sentences:

1. Simulations show cost reductions of between 4% and/to 15% and
   reductions of between 2% and/to 4% regarding the demand.
2. The method leads to improvements of between 15% and/to 54%

I always want to specify a range. Would you rather use ‘and’ or ‘to’ in these 3 examples?

I’d appreciate every comment.