Speed up a select in SQL Server - sql-server

Question

I have a table that has values like these :
Table 1 :
Name | DateTimeFrom | DateTimeTo
A | 2017-02-03 02:00 | 2017-02-10 23:55
B | 2017-01-03 14:00 | 2017-05-10 19:55
And another table that has values like these :
Table 2:
Name | Date | Hour | Value
A | 2017-01-01 | 00:00 | 0.25
A | 2017-01-01 | 00:15 | 0.25
A | 2017-01-01 | 00:30 | 0
A | 2017-01-01 | 00:45 | 0
A | 2017-01-01 | 01:00 | 0.25
[...] Contains values 0 or 0.25 every 15mins
Result :
Name | DateTimeFrom | DateTimeTo | Value
A | 2017-02-03 02:00 | 2017-02-10 23:55 | 345.0
B | 2017-01-03 14:00 | 2017-05-10 19:55 | 1202
I've created a view that contains all the columns from table 1 and the SUM of all the values from the table 2 according to the daterange on the table 1. The problem is that Table 2 contains more than 3 million rows and the SELECT takes about 10 mins...
Is there a way to speed up the process ?
I tried to create an index on the table 2 but I don't know which index (clustered ? on which columns ? ) i must create to lower the execution time.
Edit (here is the query) :
SELECT Name, DateTimeFrom, DateTimeTo FROM Table1
LEFT OUTER JOIN Table2 ON Table1.Name = Table2.Name AND Table1.DateTimeFrom <=
CAST(Table2.Date AS DATETIME) + CAST(Table2.Hour AS DATETIME)
AND (CASE WHEN Table1.DateTimeTo IS NULL THEN GETDATE() ELSE
Table1.DateTimeTo END) > CAST(Table2.Date AS DATETIME) + CAST(Table2.Hour AS DATETIME)

Answer 1

Op(Swapper) - Are you trying to only return the past 2 days?
Start with a non clustered index on table 2 date include value column.
Then add a filter for only the data set you need, no one can consume 3 million records. something like where datetimefrom > datediff(month, 1, sysdatetime()) (in the view definition)
A second thought, why compute this data over and over again via a view, consider materializing this data into a table.