select @@VERSION

declare @v varchar(max) = '{i:0;i:3947;i:1;i:4343;i:2;i:4345;i:3;i:4644;i:4;i:4627;}'
set @v = replace(replace(@v, '{', ''), '}', '');
with x as (
    select row_number() over (order by 1/0) % 2 as [rn], * from string_split(@v, ';')
),
y as (
    select 
    row_number() over (order by 1/0) as [rn2],
    v.[value]
    from x 
          cross apply string_split(x.value, ':') v
    where rn = 0
)
select row_number() over (order by 1/0) as [rn],
       [value]
from y
where [rn2] % 2 = 0

declare @t table(id int, product_ids nvarchar(100))

insert @t (id, product_ids) values
(15, '{i:0;i:3947;i:1;i:4343;i:2;i:4345;i:3;i:4644;i:4;i:4627;}'),
(16, '{i:0;i:232;i:1;i:5345;i:2;i:34534;i:3;i:1212;i:4;i:5555;}')

select 
	t.id, 
	product_ids = z.[value]
from @t as t
cross apply(values(replace(replace(replace(replace(t.product_ids, 'i:', ''), ';}', ']'), ';', ','), '{', '['))) as tt(jsn)
cross apply openjson(tt.jsn) as z
where z.[key] % 2 = 1