This game is a bloatware. I can't play it comfortably with this PC.
重いソフトウェアのことを、bloatware といいます。
(software whose usefulness is reduced because of the excessive disk space and memory it requires)
(この)ゲームが重たい
This game is a bloatware.
「快適に」は comfortably でいいので、
このパソコンじゃ快適に遊べない。
I can't play it comfortably with this PC.
となります。