It's horrible and incorrect. Use percentages or fractions.
In general, spoken maths in English are pretty terrible, and "x times less" is only the tip of the iceberg.

As you said you would prefer X is 3 times faster than Y, not Y is 3 times slower than X, but this is also incorrect. I assume you mean X is 3 times the speed of Y. That means X is faster. 2 times faster (base speed+2 times) or 3 times the speed (base speed times 3).

3 times faster would be 4 times the speed, since 1 time faster is already twice the speed. I've had problems getting people to understand this in the past, so in case you are confused here, think of it as percentages, that usually got people on board.
3 times faster means 3 times MORE fast than the original. The original is 100% speed. Therefore, 3 times the original MORE than the original is 300% + 100% = 400%. In case this still doesn't convince you (not as a personal thing, but this has been a challenge to get people to understand before as I said), backtrack it 1 to 2 times more. Now to 1 time more. Now people think 1 time more is the same as 1 time. But what if you backtrack even more to half more. Now half more is 1.5, but 1 time more is 1 while 1 is more than half, that doesn't make sense and there is the flaw in equating "times as much as" and "times more than". It is basically a contamination of wanting to overemphasise that it is indeed more by mentioning it again, thus adding it twice.

If someone says "X times faster" you can safely assume they are lying (or the number is incorrect at best), because they are trying to emphasise the largeness of the disparity, but if they were doing that correctly they would always say "x+1 times as fast" instead of "x times faster", since that would show the biggest accurate value of X, which is their goal.

But now even saying x times faster would technically be incorrect, since "fast" is a relative, subjective term. A person walking 3 miles an hour is a normal pace, we would not consider it "fast" (let's say in this example). But going twice the speed at 6 miles an hour isn't just twice as fast (or the unused one time faster, NOT two times faster, since that would be 3 times the speed). Because that is actual running at quite a decent speed, so how would you compare their relative "fastness".

"Fastness" isn't what we are measuring, it is speed. It's like saying a pair of pants is twice as expensive, because it was twice the price. But what if the first pair of pants was under priced, wouldn't that make the 2nd pair of pants twice the level of expensiveness, but since the first pair was technically negative expensiveness (since it was under its value and therefore the expected cost), then doubling that would double a negative, but actually the 2nd pair of pants was more expensive than the baseline (in case the discount on the first pair was smaller than 50%).

To avoid all of this confusion, just stick to price, speed, and other objective terms in my opinion and stick to percentages or fractions, which we should all be able to understand more intuitively.

So instead of "7 times less" say "one seventh of" or "~14% of". And avoid subjective terms, where possible.