I have 10.10.3 on my MBP and have been experiencing eratic WIFI for the last few weeks too. However, I don't use Photos and I never enabled iCloud backup (on ei

I have 10.10.3 on my MBP and have been experiencing eratic WIFI for the last few weeks too. However, I don't use Photos and I never enabled iCloud backup (on either my iPad or my MBP). So it seems like the OP may be onto something re: the actual update. Updating to 10.10.4 shortly, hopefully that makes things better.