Can I refer readers to link to a large figure?
In the journals I help edit, we receive figures such as these. Some can be extremely massive, involving high-resolution images of photomicrographs or diagnostic tests. If the figures are a necessary part of the paper, then we would insist that they be submitted to us as is and we will work with the authors to find a suitable option for presenting the work if it passes peer review. 

We have never allowed pictures or files to be hosted outside our ecosystem for two reasons. First, we have no control over those files so we will not know whether they have been modified in some way. Second, there may be issues with copyright.

I suggest that you flag this issue with the associate editor handling your manuscript for discussion following the peer-review process.

Good luck.