You also lose all that efficiency when you start to read a lot of data structures in perl, because reading data ca n increase the reference counters, thus a write actually happens in the background, causing the operating system to copy the pages.
So, don't assume stuff is memory unfriendly. Measure it. In your context, where it matters.
Also, starting a new perl interpreter takes about 0.017s "cold" on my machine, and 0.002s when cached. Compared to a 1 minute run time of a worker thread, that's like 0.03% (cold) or 0.003% (warm) - nothing to worry about.