"Love After Lockup" star LaTisha Collier's not going to love this ... she's going to prison .... because she was just given hard time in her forgery case ... TMZ has learned.

An Iowa judge sentenced the "Love After Lockup" star to 15 years in prison ... her punishment in the case accusing her of scamming clients of her financial firm.

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LaTisha was hit with felony charges of forgery and identity theft last August ... prosecutors say she used her tax-prep and bookkeeping business to access clients' money and personal information. Prosecutors dismissed the identity theft charge.

Her "Love After Lockup" story followed her relationship with Keith Collier, who was doing 14 years for distributing cocaine.

She's had her share of legal issues too ... they were both busted in November on drug charges.

Now, LaTishia is the one going to lockup.