150 orbs is roughly 75% of all orbs found in the mine. While you can certainly focus on this earlier, it becomes much easier with the Ore Detector from Vectron. Orbs are typically found at the end of caves as well as secrets, with several found by casual digging.
While there is no official counter for orbs, maxing all upgrades requires 151 orbs. If you have reached max level and Damage Reduction is available for purchase in the Dandy's shop, tally up the remaining cost in orbs to purchase the rest of the upgrades. If you have enough orbs, you are over 150.
For help finding the secrets, consult that achievement guide, which has an excellent video.