Adam Clarke on John 15:11

That my joy may remain in you - That the joy which I now feel, on account of your steady, affectionate attachment to me, may be lasting, I give you both warnings and directions, that ye may abide in the faith.

That your joy might be full - Or, complete - πληρωθη, filled up: a metaphor taken from a vessel, into which water or any other thing is poured, till it is full to the brim. The religion of Christ expels all misery from the hearts of those who receive it in its fullness. It was to drive wretchedness out of the world that Jesus came into it.

Bishop Pearce, by joining εν εμοι to χαρα, and not to μεινῃ, translates the verse thus: These things have I spoken, that my joy in you may remain - which is according to the meaning given to the first clause.