I have three older sisters and each age gap is 15, 9, and 8. You can say I was a surprise

This thread's math/nomenclature is slightly confusing to me, as it could be read differently than intended:
I'm assuming u meant- sis 1 born 15 yrs before sis 4(=pink); sis 2 born 9 yrs before sis 4(=pink) & sis 3 born 8 yrs before sis 4(=pink) - so mathematically (i am not a professional mathematician or anything related, im just a pedant n read a lot, also somewhat of a auto didactic ie self taught/self learn) it's 6 yrs between sibling 1 & 2; 1 yr between siblings 2 & 3; n 8 yrs between siblings 3 & 4.unless u actually mean tat when ur eldest sis was born 15 yrs before sis 2, sis 2 born 9 yrs before sis 3 n sis 3 born 8 yrs before u; so when u were born sis 1 was born 32 yrs before u. Tldr: I assume sis 1 was 15, sis 2 was 9 yrs old n sis 3 was 8 yrs making it (in mathematical notation): 6,1,8 yrs age between sib 1 & 2; 2 & 3 n 3&4[which makes sense in these days]
My eldest bro is 4 yrs older than me n my younger brother 1 yr n 10 days younger than me(so longest gap is only 5 yrs between my older bro n younger bro, Asian families of my generation [maybe even 5-10 yrs before I was born] hv fewer succeeding offspring each generation-my aunts and uncle I think had 15 yrs or more[20 yrs ?] between eldest and youngest [n my youngest aunt is already retired, so it's quite long ago] while current generations my bro(s) n cousins hv mostly 2 or 1 offspring(my younger cousins aren't married/hv family yet; I'm talking abt 15/25 yrs younger than my age [my parents cousins children I mean; my parents sibs children are either already married with kids or not married/no kids].
Srry for long reply: tldr 4 yrs, n 1 yr between my older bro n me n me n my younger bro, just 3 of us in total