Do you see the plus signes being chopped off in the TOC? You do not see that in Firefox... There is code to fix it but I don't know where to put it. It goes something like this...
<td width="172"><strong>SBP2:</strong></td>
<td width="62"><label for="sbp2"></label>
<input name="sbp" type="text" id="sbp2" size="4" maxlength="4" style="width: 40px;"/></td>
If you grab the frame bar and resize it back and forth, it fixes itself but not everybody would know to do that.
Take a look at post#2 in this thread - Re: Default size of WebHelp TOC Pane
BTW - I think you're looking at the help using Edge, not IE11 - there have been issues reported with newer builds of Win10 that have thrown off Edge compatibility with RH2015 - see Re: RH 11 Webhelp on MS Edge: TOC disappears after search