100iv Lapras

I'm in a same boat. 91% iv, is/b. I decided to max it and lvl another with fb/b, maybe 3rd shall be fb/ib

Save it. Ice Shard was the best defensive quick move (and still is, just defense isn't worth much). It's not far behind Frost Breath, just a little slower and a little less energy, but works way better with the Gym AI. And we don't know what the future will bring - PvP, breeding, or something else. Finally, a Quick TM could leave you with WaterGun, requiring another to get to Frost Breath. Not worth it, to spend on average 1.5 QTMs for a small gain.

My 100% Lapras (hatched like all 4 of mine) has WG/Blizzard. An easy fix to FB/B with a Quick TM, when I have enough of them to spare one for that. My highest level Lapras has IS/BZ. More at issue is getting candy to bump her up to level 31.

I have a lapras with same moveset as you. I will go for IS/IB. And I actually do that by using 3 charge TMs. Hope it helps.

I suggest you save your resources and do not use it on Lapras. Lapras is not a top-tier attacker now. Among ice-type attackers, Articuno is obviously better and also attainable, and Jynx deals damage much faster although with lower bulk.

I have only 1 IS/IB Lapras, but with 0 attack stat. I don't have any other IS Laprases.
I have a 88% Lapras with almost 2k CP, but with WG/HP.

If not for the risk of getting Hydro Pump, I would use a charge TM on my Ice Shard/Blizzard Lapras. Don't have enough charge TMs though to be able to waste several trying to get Ice Beam.