I still don't get why it takes 15s for you to execute that code, it runs in 3s on mine. Did your machine swap to disk or something? Or is that an ancient machine? or a debugging perl?

A few thoughts anyway:

1. Try to pack vector. You're only accessing it linearly anway

2. Try not to use that vector at all. You can populate your %pos hash in the first place instead

3. Store the data structure on disk once, for example in a BerkeleyDB. It seems to be constant, so you don't actually need to calculate it every time your program starts. Or store $wektor in a plain binary file after you created it, and in subsequent runs only retrieve that from disk and generate your hash from it.