“A transition-expression and a debater's phrase” (Morison). The use of this phrase points to Paul's training in the Rabbinical schools, where questions were propounded and the students encouraged to debate, objections being suddenly interposed and answered.
Shall we continue (ἐπιμένωμεν)
The verb means primarily to remain or abide at or with, as 1Co 16:8; Phi 1:24; and secondarily, to persevere, as Rom 11:23; Col 1:23. So better here, persist.