By default, openLCA uses less than 4GB RAM even if your computer has more memory. Unless your colleague manually changed the amount of memory allocated to openLCA, he is not using all his memory. ... thus said, 4GB is enough for openLCA but of course the calculation time of your product systems depend on a) amount of memory allocated and b) complexity of the product system. You are only likely to run into troubles with RAM if you use really large databases e.g. comprehensive input/output databases such as Exiobase or PSILCA.
I have allocated 26624MB RAM to my openLCA installation which is probably much more than most users have. In parallel I run another instance of openLCA with just 4GB of RAM which works just fine too.#
I hope this helps.