Multiworld Lag Qestions

Hello, I was thinking of using the multi-world tool on my server and adding the nether but I have a few questions before I use it.

#1. Does the second world add lag? any more stress on the server?
#2. does the transition add lag?

 

I can tell you for sure that having a second world will require more ram.
More worlds = more ram allocated by the server

I had really bad experiences using multi world, havent been able to make it work properly yet.

 

Ok because I have given the server 1.5gb but for some reason it only uses about 1gb and starts to lag..

 

Hmm, we have 4 worlds and nothing seems to lag, haven't seen any increase in ram aswell :/

 

well I could probably handle 2 servers if it decided to use ALL the ram and not just half.