[raztoki]

your using 5 chunks currently (parts of files), it breaks up the file into 5 pieces and http requests those 'chunks' from the server. As not all parts have the same speed, some will finish before others, leaving one or some slower chunks to finish. If you right click properties the file, you can see which is what. 15/15 sounds like activity statistic of the package. What happens with speeds, and performances if you used a wired connection over wireless?

If you stop the download and resume (as your premium user) it could improve the last remaining chunk.