No, it's not surprising that we've committed to the level of spending shown so far. Anything less would likely mean our stay in the Prem would be just for a season - i.e. literally doing a Fulham by not doing a Fulham.
And it's worth noting that the suggestion of "a total gross spend of near £150m", and it's a matter of opinion whether that is astonishing or not, isn't likely a gross net spend now. Rather, it's a commitment to spend that on a number of assets across a payment period negotiated for each one.
Potentially, some assets will appreciate in value and may be sold at a profit before we've even fully paid for them which could mean they've effectively cost us nothing at all. For example, if we sell El Ghazi next year to, say, newly-promoted Brentford or Bristol City for £30m (), not only will we possibly not have even paid the final installment on him at that point and not only will he have cost us nothing, we'll actually make on the deal.