Regarding texting being very slow.
You need to delete alot of text messages and this will stop. This happened to me and a friend of mine who also has an S5, but in my case only to my most frequent contact. After I deleted hundreds of messages to and from them it was fine. It seems especially sensitive to MMS texts and texts that are URLs.
First thing to try is to go to Application Manager/Messages and delete the cache under "Storage". If that doesn't work, you will have to delete text messages. I deleted hundreds of old messages from my contact that was a problem and it was alot better but still a bit slow. Once I deleted a bunch of images we texted back and forth, it was back to normal.
now that i've updated to Marshmallow, i've rooted my phone 🙂 i was waiting to root until the upgrade rolled out and found a handy guide for the Rogers S5