Well, yes, really only bits :)
I suspect that Laris(s)a can't be among the most popular names, say the Top 10, because the following table of popular Russian names does *not* mention it:
http://www.imena.org/mias1996.html
The following table from 2004 of the names of the students of a Russian university in the Far East has the name on rank 25:
http://www.amursu.ru/spravka/names.html
Larissa seems to be popular as well in my country: In the hitparade of names for newborns in the
German speaking part of Switzerland of the year 2000 it is on rank 23 - but that wasn't the question, was it :)