(Please excuse my English - I don’t speak Spanish)
Japanese has a very fast “syllables per second” count just due to the sound system where it is pretty much always consonant+vowel pairs with occasional longer vowel sounds or a final ん. This doesn’t mean that Japanese conveys more information in the same amount of time though. The study I’ve seen that measured “information per [time]” found English to convey more information in less time despite being a “slower” language (in terms of syllables per second) however the study was pretty bad in my opinion as they used the same text translated into all the languages tested but only a single text. There is a clear problem here given that the way of phrasing something or the formal grammar used in a written text could happen to be “slower” for that specific text but not in general or not for casual speech, etc. It’s pretty clear without thinking too hard that some things can be conveyed much faster in Japanese than in English or Spanish and other things may be slower.
Interestingly whenever I broach this topic with Japanese people they tend to believe Japanese is slow and clear precisely due to the consonant+vowel pairs giving quite clear delineations between “syllables” and they find English to be very “fast” because of the lack of clear delineation (from their perspective).
My opinion is that when learning a language it will always sound “fast” whilst you don’t understand it properly and these kind of studies about speed don’t tell us anything valuable as learners.
Perhaps also relevant to this thread, it is not uncommon to hear Japanese people claim Spanish has “easy” pronunciation for Japanese speakers (and vice versa) but the few times I’ve heard Japanese people speak Spanish they’ve had a noticeable Japanese accent and the only time I’ve heard Spanish speakers speak Japanese they’ve had a very strong Spanish accent, although admittedly they were clearly beginners in both cases. The intonation (pitch accent) and the vowel sounds were the main culprits in both cases which is also normally the same issue native English speakers have.
(also feel free to reply to this comment in Spanish if you want to continue the discussion - I don’t want to accidentally turn this into an English thread, sorry!)
I literally have to reteach myself spanish in my spanish class 
so now I try to learn japenese by hearing the spanish definition of the word so I can train both my spanish and japenese :3 I actually think that its a really good system tbh.
). It’s not perfect, of course, but I do think we share many sounds and that makes it easier compared to other languages like English.
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