The ESP Guitar Company

You could get the transformer in the amp replaced. Reckon it would cost maybe 200-300 Euros.

yep, something like that... The transformer I bought was like 40 or 50 so I went with that

he wall outlets' circuits in houses and in venues will have different maximum wattage ratings (usually between 1800-2400 watts)IDK where you got that information but it is wrong:a typical duplex or even a GFI receptacle is rated at 600 watts max per duplex(meaning it has 2 spaces to plug 2 items into). 2 of those would be max 1200 watts. You'd have to have 4 GFIs on the same line to get 2400 watts.. understand?

It is also rated at a 15 Amps, which is precisely why most older houses in the US require more fuses rated at 15 Amps than at 20. The 20 amp fuses are for larger high drain items such as the refrigerator, microwave, toaster, and such.

It's not really about wattage per outlet anyways,, its about the pure amps of power being allowed to that circuit, which is defined not only by the circuit breaker, or fuse, in the box at the main electrical box where it is wired to but also the guage of wiring used.
This can be changed at will with the right tools and most importantly the right wire. The wrong wire, or circuit breaker(or fuse), or any number of things drawing too much current will eventually start a fire, so changing these at random(especially fuses) without the know how will get you into trouble faster than Wile E. Coyote spying a roadrunner.

As for that asshat tech saying 'your amp has a bass & treble response so buy the larger xformer & I'm not trying to push you into a sale you don't need" ... it's PURE BULLSHIT. They guy IS trying to soak you needlessly & not help you. Any GOOD hardware store would be able to help you with this properly or at least refer you to an electrician that either knows the proper way or can refer you to someone more acquainted with electronic devices(as opposed to house/building wiring, which they would most likely know better). ALSO, considering that the 5150's EQ is PASSIVE... and not Active your amp can only CUT frequencies & not Boost them.
Passive cuts & Active boosts. Period. HOWEVER, the Resonance & Presence ARE ACTIVE within the POWER AMP ONLY, so that should be taken into consideration some.

Something else I must say is that since you are in EU, the ratings I stated for GFIs may not apply, but I doubt it.

In the end I say good luck & go with your gut about the transformer... hell,, if you're staying/playing in EU all the time,, just save yourself some loot/headache in the long run & just swap out your amps power transformer o its 220V.. OR do like I originally suggested by making the new power Xformer 120/220V system.. you could even make some money on it in the long run if you sell it becuz it would work in EU or US.

If you want even more versatility & are willing to shell out the big bucks have the amp modded so it accepts both 6L6(like it does now) and EL34s.. why Peavey didn't do that to begin with I'll never understand, can you say TripleXXX/JSX = lesson learned? lol
peace

trust the electricians. there's no money/prize in it for them.. just an honest evaluation & your friendship.