If anyone honestly think the GOP would impeach Trump, you're either naive or insane.
We don't need the whole GOP. Just enough to hit 218 in the House and 67 in the Senate. A tall order, but midterms + a hypothetical indictment make it much more attainable.
Would 15 GOP senators vote to impeach?
I think if there was a recorded conversation then yes they would
That, plus it'd depend heavily on public reaction. They may bash the polls, but they definitely don't ignore them. If Trump's numbers and, by not impeaching him, their numbers begin to plummet, you'll see them jump ship faster than you can imagine. They're committed to their agenda - not Trump. He's simply there to sign what they send him. They have no loyalty to him, but they know a sizeable percentage of the population - and their base - do. So, it all comes down to the numbers.
Anyway, this is an investigation and we must wait to see what fruit it bears. If they find Trump guilty, then all hell breaks loose. But there is a good chance they either lack the evidence or he simply is not guilty of obstruction of justice.