Poor performance of couchbase on a single machine

I’m trying couchbase for my project but the response time for queries are too slow, It takes about 9 min without indexes and about 1min with index.
I have already talked with @geralss about it on stackoverflow:

I’m using a single machine, I have read that couchbase will not performance very well with one machine, but I have just 2,5GB of data on a machine with 16GB of RAM. My bucket have 3.5 GB of RAM.
I’m using couchbase 4.5 beta
There’s another way to increase performance instead of use couchbase on more than one machine?