iTunes quits in internet radio stream mode after display goes to sleep

i have my display set to sleep at 15 minutes and after it sleeps iTunes quits when i am listening to internet radio stream. hard drives are set to sleep when possible and wake for network access is enabled. iTunes V12.2.1.16 OS X V10.10.4 Mac mini (Late 2012) Processor 2.3 GHz Intel Core i7 Memory 4 GB Storage 1TB Display AOC (Intel) 2236

Thanks!