Split dose 7.5 + 2.5 pens

I'm on a 7.5 pen and an contemplating going up to 10 as by day 5 I'm definitely not feeling the effects like I used to ( 2 months on 7.5). My partner decided to go off MJ the day after I ordered his next 2.5 pen. What would be the effect for me of a mid week 2.5 vs going up to 10? This is more about not wasting ££ on this extra pen.