What is a normal file copy speed for SSD?

Sounds like you think all SSD's are equal (or near equal) which is not true. See, for example these benchmarks

Also the speed is not just dependent on the SSD.

But no, I would not consider 5MB/s to be particularly fast.

For example, the last real copy I did that I can remember (around 2GB and 10,000 files) was reported by Windows as around 40MB/s. (This is on an Intel SSDSA2M080G2GC SSD which is over a year old and hence may not be particularly fast)

HD Tune: INTEL SSDSA2M080G2GC Benchmark

Transfer Rate Minimum : 88.8 MB/sec
Transfer Rate Maximum : 221.3 MB/sec
Transfer Rate Average : 210.0 MB/sec
Access Time           : 0.1 ms
Burst Rate            : 144.8 MB/sec
CPU Usage             : -1.0%

Maybe your SSD garbage collector is full and overloaded. Transfers to SSD tends to be better if you put your SSD in idle for some time. Howerver you could try a firmware upgrade for it.