Acrobat Reader ISO (for iPad) don't do forms
https://itunes.apple.com/us/app/pdf-expert-fill-forms-annotate/id393316844?mt=8 this is the only program for now that does PDF Forms on the iPad.
I find the same issue using both Acrobat Pro X and Acrobat Pro XI.
What I found to be contributing factors are:
1. programs running in the back ground
See what is running in the background and stop what is not required.
2. the overall size of the form (MB)
under “File”, “Save As” there is an option to Reduce Size of PDF.
I found this to help on some mobile devices.