Is dram constantly refreshing during windows sleeps?
Modern DRAM such as SDRAM, DDR ... DDR4 have an "automatic self refresh mode" where the memory just need to be powered to internally manage periodic refresh cycles. The rest of the computer can be powered down to save energy.

In that mode, DRAM draws about half the normal idle current and 1/5 to 1/10 of the current drawn during reads.

(DRAM refresh period is in the order of 20ms, so it's impractical to periodically awake the computer just to refresh DRAM.)