And while he admits it was a special day in Belfast, he realises this Saturday could be even better, playing in front of Scots aplenty.
"It was a great feeling," he told Glasgow Warriors' official website when speaking of that memorable triumph.
"I remember Leone (Nakarawa) bursting through about five or six tacklers and then passing to me when everyone was beaten, so it wasn't really much to do with me!
"It was great to score, though. We had tremendous travelling support that day, so I'm sure that'll only be greater given we're playing in Glasgow this time."
Harley is one of several players still at Glasgow from that 2015 win and the 28-year-old feels that should help them in such a massive game.
"It's hard to compare the two teams against each other," the back-row said.
"I think what will benefit us is the fact that we've got a few boys who have played across both teams, so they'll remember the feeling. The last time we went out and played well and weren't inhibited by anything, so we'll be training this week ready to hit our stride this weekend.
"If you look at the way we've been playing over the last few weeks, we've really focused in. We know that we have the quality in the side to go on and win the title - we've talked about it all year and we're now one game away. It's what the whole squad has been building towards all season."
On the prospect of running out at Celtic Park, he added: "It's great to play in a final in Glasgow.
"The semi-final was special with that bit of extra noise from the extended stands at Scotstoun - the crowd were excellent, urging us on from the first minute. That's something we can look forward to on another level this weekend.
"Celtic Park is a great stadium. We're really looking forward to packing out the stadium with our fans - last time we played in the final in Belfast it was like a home game for us with the number of our fans that made the trip, so we're really looking forward to this weekend."