Katleen - are you sure you mean 7.5cm, that's 3inches or do you mean 7.5mm, if so you can adjust to the MM difference, but you cannot walk with a 7.5cm difference, you are going to damage discs in your back, and you don't want to be doing that, believe me, it is extremely painful.
How do I know this, I have a 22mm or 2.2cm difference, that's about 3/4 inch, added to my left hip, and the hospital did not want to know, firstly they denied I had an issue, and when finally I was able to prove I had an issue, at my own expense, it seemed it was my fault for not telling them I already had a longer leg between the knee and heel that I was unaware of, had grown with it my entire life and never caused me any trouble, but it did explain why I was told I always ran like a duck.
My best advice came from a physio, very senior physio, who measured my legs correctly, and came up with almost exactly what a later LONG-LEG-XRAY confirmed, I had 22mm in total, 10mm naturally, and 12mm added by the surgeon.
In the meantime I had been attempting to walk as I was, and ruptured S1-L5, bulging L5-L4, and bulging L4-L3, causing me immense pain sciatica, I still have it I'm afraid the damage is done, hospital also denied there was a link between LLD and back problems.
Can I suggest to you get that measurement done ASAP, with a physio, and or shoe fitting specialist, rather expensive, for a start, then find a heeled shoe that lifts your foot at the heel and lifts you the amount of the discrepancy, as in normal walking it is your heel you put down first, that at least will even you up, and hopefully avoid the back problems I have.
I have a shoe lift that fits in most of my shoes, and for around the house, barefeet, I walk on my toes, on my right side, now the shorter side, but every night I make a point of stretching my Achilles tendon to make sure I am not shortening that tendon and creating more problems for myself long term.
Oh my god I cannot believe they have got it that wrong, get a lawyer and start legal procedings especially if it is 3 inches, not acceptable even if they can fix it.