You may find this interesting: https://2009-2017.state.gov/m/fsi/sls/orgoverview/languages
This results in a weird paradox: for literate Russians it is easy enough to read written bulgarian but almost impossible to understand the spoken language.
The aspects that make languages difficult for a native English speaker vary quite a bit with the language. I would expect individual experiences with the languages to have high variance as a consequence.
E.g. both Turkish and Russian are in Category 3, but Turkish is trivial compared to Russian.
Turkish grammar is extremely regular, and follows easily defined rules that fit about two pages of easily digestible tables.
In comparison, Russian is a separate class tought in Russian schools for four years to native Russian speakers. And you still get people who can't properly inflect numerals, for example.
"I want to swim" in Russian is "ja hoću plavatj", "I" + "want" + "to swim". The only difficulties are the conjugation of "want" and the aspect of "to swim". In Turkish it's "yüzmek istiyorum", where "-mek" is "to" and "-um" is "I". Even if the system itself is straightforward, it's still alien to a native English speaker.
As a native Russian speaker who speaks English and Turkish:
The question isn't about alienness. It's about difficulty. Turkish is trivial compared to Russian. You can learn all the grammar rules you'd ever need in a week or so (though most study materials make it harder than necessary). The rest is just learning vocabulary. Which is just as alien to an English speaker as Russian.
As for the example...
Here's a valid three word sentence in Russian: Ya idu domoj (I'm going home).
Depending on context, mood, feel, etc. any permutation of those words is a valid sentence: ya domoj idu, idu ya domoj, idu domoj ya, domoj ya idu, domoj ya idu.
And that's before we get into inflections, conjugations, gender etc. that neither English nor Turkish have. Or somewhat arbitrary pronunciation rules (korova is pronounced kahrohva) whereas in Turkish every word is pronounced exactly as written (with very few quite regular contractions in regular speech like yapacağım -> yapıcam) etc.
The original link is specifically about difficulty to native English speakers, which is certainly linked to its alienness.
Russian: extremely complicated grammar using concepts entirely alien to English (declensions, inflections, conjugates, grammatical cases, genders, transgressives, and even plurals are weird), has free-form-not-really sentence structure, jumping stress. Oh, and a completely different alphabet to boot.
Yes, phonetic spelling but you won't be able to read anything much before WW1.
Note: 99.9% of Turks are not able to read much of anything before WW1.
All through middle and high school, so for 7 years from around 10 to 16. It did become one eventually in primary school, so probably the last 2 or 3 years there.