Playtex ventaire bottle help😭😭😭

My daughter was on dr brown I switched her to playtex ventaire with slow flow nipple but the nipple is too slow and I was wondering Can I put her on a fast flow nipple at 2 months ? I switched because it takes her 1 hour to finish a bottle with Dr. Browns and it’s so many pieces to clean and with playtex slow flow nipple takes her almost 2 hours I’m trying to fix the problem idk what to do should I just put her back on Dr. Browns or get a faster nipple please help I’m stressed out because she’s gaining weight really slow only drinking 3-4 oz at 10 weeks