First bit "Plus 5 (or Plus 10)": refers to speed above Vref
Maybe - maybe not. Depends on the operators SOP and they vary significantly from pure cant to something you can rely upon as being accurate and concise. The speed call could be the knots above or below the selected approach speed. Or it could be above or below Vref. Big difference.
If due to gusty winds the pilot elects to add 15 knots to Vref and aim to fly on final at that speed, then the SOP call could be Plus 15. On the other hand if the call is based upon variance from selected approach speed there may be no call needed. If however the call is again based upon selected approach speed and the pilot is lightly faster say by 2 knots - then the call could be Plus Two.
Plus 2 (above selected approach speed) doesn't raise eyebrows with most pilots under these conditions but a call of Vref Plus 17 may cause concern if the runway length is limited or surface slippery. What affects the landing is the number of knots in excess of Vref.
Regardless of the above, there is nothing more annoying and dangerously distracting than the PNF keeping up a more or less continuous chatter of unnecessary calls. It may sound good on the voice recorder and keep the legal people smiling, but there is no flight safety value at all.